Field of the Invention
This invention relates to illumination and projection technologies, and in particular, it relates to a light emitting device and related projection system.
Description of Related Art
Using a blue light to excite a yellow phosphor material to generate a yellow light, and then dividing the yellow light into a green light and a red light, or combining the yellow light with the blue light to generate a white light, are commonly used techniques for light sources in current projection and display fields. However, currently used yellow phosphor material is usually a YAG (yttrium aluminum garnet) phosphor; in the yellow light generated by YAG phosphor under excitation, the component in the red wavelength range is relatively weak, so that when such light is used in projection and display applications, the red light generated by light division or the white light generated by light combination are not completely satisfactory.
One solution in conventional technology is to supplement a red light in the yellow light generated by the phosphor material. For example, FIG. 1 illustrates the structure of a conventional light emitting device. As shown in FIG. 1, the light emitting device includes a blue laser source 110, a red laser source 120, filter plates 130 and 140, a reflection type color wheel device 150, a lens 160 and a light rod 170. The filter plate 130 reflects blue light and transmits other lights. The filter plate 140 transmits yellow light and reflects red light. The excitation light emitted by the blue laser source 110 is reflected by the filter plate 130 to the wavelength conversion device 150. The wavelength conversion device 150 includes a yellow phosphor, which absorbs the excitation light and generates a yellow converted light, which transmits through the filter plate 130 to be output along an optical path separated from the optical path of the excitation light. The filter plate 140 is located on the optical path of the yellow converted light outputted by the filter plate 130; it is used to combine the yellow converted light and the red laser light, which are respectively incident on the two sides of the filter plate 140, into one light beam. The combined light beam is collected by the lens 160 and homogenized by the light rod 170.
However, in this device, because the converted light emitted by the phosphor material has a Lambertian distribution, while the laser light has a Gaussian distribution, the combination of the two light beams is not uniform. Even after mixing by the light rod 170, its uniformity is still unsatisfactory.
Meanwhile, with the ever increasing requirement for high brightness of the light emitting device, the power required for the blue laser source 110 is higher and higher. This requires the blue light source to use more laser diodes, which increases the light emitting surface area of the blue light source. On the other hand, the red laser source 120, which acts as supplemental light source, only requires a relatively small amount of light, so the cross-section area of the output light beam of the red laser source 120 is relatively small.